The present specification generally relates to relates to Long Term Evolution Advanced (LTE-Advanced, LTE-A) system which will be part of 3 rd Generation Partnership Project (3GPP) LTE Rel-12. More specifically, the present specification focuses on signalling arrangement related to flexible downlink (DL)-uplink (UL) traffic adaptation in TD-LTE.
Time division (TDD) LTE (TD-LTE) Rel-11 supports UL-DL reconfiguration only with periodicity of 640 ms or longer. The goal of Rel-12 is to enable faster time division duplexing (TDD) UL-DL reconfiguration. The question is how to provide the necessary signaling mechanism(s) such as hybrid automatic retransmission request (HARQ)/scheduling timeline for user equipments (UE) supporting flexible UL/DL mode.
According to 3GPP document R1-130421, the candidate set for TDD UL-DL configuration is defined in the following way. Namely, only a UL subframe or a special subframe which is followed by an actual DL subframe can be changed to a DL subframe, while it is not allowed to change a DL subframe to a UL subframe or special subframe. Further, no new TDD UL-DL configuration is introduced, and TDD reconfiguration can only happen among existing seven configurations. In addition, candidate TDD UL-DL configuration is defined for each of existing seven TDD UL-DL configurations as shown in the table below, illustrating a definition for candidate TDD UL-DL configuration.
SIB1 IndicatedTDD UL-DLCandidate TDD UL-DLConfigurationconfiguration set00, 1, 2, 3, 4, 5, 612, 3, 4, 523, 4, 534, 5455NA61, 2, 3, 4, 5
The biggest advantage of such approach may be that legacy UE's channel state information (CSI) measurement is kept unchanged since DL frame is not used as UL subframe. The disadvantage of this approach may be that it does not consider potential limitations caused by the signaling solutions at all.
Document 2010E02547 FI (“HARQ design for dynamic UL/DL allocation in backwards compatible LTE-TDD”) introduces a reference configuration method. More detailed illustration of such reference configuration method can be found in 3GGP document R1-130130. FIG. 4 (as adopted from 3GPP document R1-130130) shows a schematic diagram of subset relations for UL and DL subframes, in particular the subset relation for DL and UL reference configurations as a function of UL-DL configuration. For example, a relation D(1)→D(2) means that DL subframes in configuration #1 form a subset of DL subframes in configuration #2. Accordingly, for example, the relation U(2)→U(1) means that UL subframes in configuration #2 form a subset of UL subframes in configuration #1.
According to 3GGP document R1-130130 it is possible to vary UL-DL configuration, m, to the UE as long as long as D(A)→D(m)→D(B) or equivalently U(B)→U(m)→U(A).
It is noted that 3GPP document R1-130130 provides just a high level principle for defining the properties of UL-DL reference configurations. It does not provide a working solution for dynamic UL-DL configuration adjustment in TD-LTE cell having legacy UEs in the system.
The main problem is identified as what is a complete solution for a reference configuration based method supporting scenario having both legacy UEs as well as flexible UL/DL mode UEs operating simultaneously in the same TD-LTE cell.
Hence, the problem arises how to define the possible UL-DL configurations that can be applied with each of the different (seven) UL-DL configurations defined by the system information block number 1 (SIB-1) (which is followed by the legacy UEs). Further, the problem arises how to define UL/DL reference configurations with an UL-DL configuration defined by SIB-1. In addition, the problem arises what signaling mechanisms are needed.
Hence, there is a need to provide for reference configuration for flexible time division duplexing.